This invention relates to an apparatus for treating a liquid and particularly relates to an apparatus where liquid is treated using a radiation source such as an ultraviolet lamp.
The invention will be described with reference to an ultraviolet (UV) lamp but it should be appreciated that other radiation frequencies are also envisaged.
It is essential for health and hygiene purposes that water and other consumable liquids are at least partially sterilised or otherwise treated prior to consumption.
One type of treatment involves the use of heat to sterilise any bacteria in the liquid, but treatment of large volumes of liquids using heat is energy intensive and requires large heaters and other capital equipment.
Chemical sterilisation is also known and used, but some chemicals interfere with certain types of liquids (i.e. beverages), and the public does not wish to consume large amounts of chemically treated liquids.
Apart from consumable liquids, sterilisation for hygiene purposes is also required in the sewerage industry and for treatment of effluent, grey water and the like.
Certain pharmaceutical and medicinal preparations and also liquid-based and require sterilisation before injection or consumption.
It is known to treat liquids using sterilising gases. One type of sterilising gas is highly reactive ozone gas. Ozone is however toxic and great care must be taken to ensure that the ozone levels in the liquid are not exceeded. Certain sensitive liquids such as milk or some pharmaceutical preparations may also be adversely affected by reactive gases. The generation of ozone reqires fairly expensive equipment and a fairly high input of energy.
A safer way to treat liquids is to use a radiation source. It has been found that UV radiation is effective in killing bacteria, algae and the like. However, UV sterilising units have to date met with limited success as difficulties have arisen with ensuring that the liquid is fully exposed to the radiation.
To achieve an acceptable level of radiation density in the liquid to be treated, it is known to provide a radiation emitter in the form of a tube which sits inside of a larger tube or housing through which liquid flows. The liquid therefore flows about the tube containing the radiation emitter and the radiation can pass into the liquid.
However, when treating grey water, effluent, waste water, bore water, or other liquids containing salts and impurities, it is found that the impurities form a scale on the surface of the UV emitter which greatly reduces the radiation density in the liquid.
Because of the difficulties associated with scale or impurity build up on the radiation emitter, the use of this type of technique to sterilise water has not found wide commercial success.
European patent specification 467465 describes a steriliser having a number of parallel tube-like lamps. The lamps are scraped clean by a scraper which is secured to a supporting plate. The plate is reciprocated along the length of the tubes via a drive motor mounted in the box. This arrangement clumsy and complex and requires the existence of motors and a power source. This specification does not disclose a cleaning device which is moved by the flow of liquid passing through the passageway.
European patent specification 648711 describes a UV radiation apparatus again having cleaning devices which are moved up and down using pull cables. Complicated signalling means are present to signal when the cleaning rings are at the end of the treatment stretch. This arrangement is again complex, expensive and requires physical driving devices.
International patent application WO 94/20208 describes radiation treatment of a flowing fluid. The treatment apparatus has a cleaning sleeve which moves between a retracted position where the fluid source is exposed to a flow of fluid to be treated, and an extended position in which the sleeve covers the source. The sleeve defines a chamber surrounding the source in the extended position and is supplied with a cleaning solution for removing undesired materials. In this arrangement, a separate cleaning solution is required to clean the UV lamps.
Soviet Union patent specification 1669869 describes a water treatment apparatus having a scraper cleaner which is attached to a rod and where the rod is lifted up and down to manually scrape the lamp. In this arrangement, the cleaning device is unable to move and clean the emitter by the flow of liquid passing through the passageway.
German patent specification 3710-250-A describes a UV water sterilising device where a cleaning brush moves along the lamp but requires a feed screw and a reversible motor to move the brush in both directions.
German patent specification 4225630 describes a self-cleaning oxidation chamber having a complicated wiper system to clean the tubes. The wiper system has one wiper unit on a plane at right angles to the first tube and a second wiper unit on a second plane at right angles to the tube axis, with an elastic linkage to hold both wipers from each other when relaxed but giving elastic pliability under pulling or compression tension. The wipers act as a piston when fluid pressure bears on them in the tube with the first wiper being denser than the second wiper. This arrangement is extremely complex and does not lend itself to simple reliable action.
The present invention is directed to an apparatus which can improve the efficiency of the use of radiation to treat liquid by reducing or possibly eliminating build up of scale or other impurities on the radiation emitter. The present invention is also directed to an apparatus which can provide a more efficient passage of liquid around the radiation emitter.
In one form, the invention resides in an apparatus for treating a liquid, the apparatus comprising:
a housing having a liquid inlet, a liquid outlet, and a passageway through which liquid can flow;
a radiation emitter which has a radiation transparent window to allow radiation to pass into and treat the liquid passing through the passageway; and
a cleaning device which cleans at least part of the window at periodic intervals.
Throughout the specification and claims, the term xe2x80x9ccomprisingxe2x80x9d is not meant to be used in a limiting form and is meant to include an apparatus having at least the features listed but the term xe2x80x9ccomprisingxe2x80x9d is not meant to limit the apparatus to only those features.
In another form, the invention resides in an apparatus for treating a liquid, the apparatus comprising:
a housing having a liquid inlet, a liquid outlet, and a passageway through which liquid can flow;
a radiation emitter which has a radiation transparent window to allow radiation to pass into and treat the liquid passing through the passageway,
the housing having means to cause the liquid to adopt a spiral flow about the radiation emitter.
The apparatus can be used to treat liquids such as water including drinking water, bore water, pool water, grey water, effluent and sewerage; although other types of liquids are also envisaged such as beverages (i.e. beer, wine and the like).
The housing may be configured such that the passageway is of a sufficient length and/or cross-section to allow the desired amount of liquid to flow through the passage while still being treated for an acceptable period of time. The resident time of the liquid in the passageway which is treated by the radiation emitter can vary depending on the degree of sterilisation required, the type of liquid, and the type of radiation emitter.
Typically, the housing is elongate having a liquid inlet adjacent one end and a liquid outlet adjacent the other end with the housing being substantially hollow to define the passageway through which the liquid can flow.
The type of radiation emitter can vary depending on the type of liquid to be treated. For liquids which are substantially clear (i.e. water, beer, white wine), the radiation emitter can comprise a UV light. For other types of liquids, a different type of radiation emitter can be used provided that the radiation is of the type to treat the liquid for instance by reducing the bacterial count.
Typically, the radiation emitter is a UV light. The UV light is normally an assembly comprising an outer glass cylindrical thimble in which the UV lamp is inserted. The thimble is sealed and presents an outer protective UV transparent wall.
To ensure maximum amount of radiation contact with the liquid, it is preferred that the UV light is positioned in the passageway and substantially in the middle of the passageway such that liquid can flow around and about the UV light. A number of radiation emitters can be placed in the housing and the position of the radiation emitters can be varied to suit the type of liquid to be treated.
The cleaning device is used to clean the window of the radiation emitter at periodic intervals. If the radiation emitter is a light assembly comprising the outer thimble, the cleaning device can function to clean the walls of the outer thimble, which comprises the window.
In one form, the cleaning device moves across the window and is actuated by the flow of liquid through the passageway. In this form, no springs or power supply is required to move the cleaning device across the window.
If the radiation emitter is a tube, the cleaning device can comprise a collar or turbine which extends about the tube and can move along the tube with the flow of water.
It is preferred that the housing is in a substantially upright or upwardly angled position and that the cleaning device is freely movable over the radiation emitter such that the cleaning device naturally falls under the influence of gravity to a lower portion of the housing. Once liquid is passed into the housing, the liquid pushes the cleaning device up and along the radiation emitter to wipe it clean. It is preferred that the cleaning device can pass to a position above the liquid outlet under the influence of liquid flow such that it does not present an appreciable barrier to movement of liquid through the passageway.